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Full text of "Metallurgy Of Cast Iron"

CHAPTER XXV.
THE   IMPRACTICABILITY   OF  HARDNESS TESTS FOR GRADING PIG IRON.
A drill test was advocated, at the close of 1900, as
being 'practical to define the grade of pig iron or the degree of hardness it would impart to castings. There are foundrymen today who could be misled into believing such a system practical, "and would buy the machine advocated for this work. A hardness test for pig iron is no more or less than judging iron by the appearance of its fracture, a method which has been in vogue for a century but now known to be wholly erroneous. There are two ways of producing different degrees of hardness in pig iron or castings, one is by varying the percentages of silicon, sulphur, manganese, and phosphorus in iron, the other by varying the rate of solidification and cooling to a cold state, also shown on pages 167 and 168. Alterations in either of these factors can cause the carbon to take the combined or graphitic form. The higher the combined carbon the harder the iron, and the more the graphitic carbon is in evidence the softer the iron.
An illustration of what may often be expected in the differences of hardness between two casts of pig iron that would give like grades or softness in like castings, is seen in Nos. i and 2, Fig. 43. Were these samplesstings.    The pig samples seen in Figs. 40, 41 and